There have been disclosed in Japanese Patent Laid-Open No. 9-87215 (1997) a method for oxidizing cycloalkanes by allowing cycloalkanes to react with oxygen-containing gas in the presence of an imide compound and a ruthenium compound, and in WO9940055 a method of allowing cyclohexane to react under an oxygen atmosphere in the presence of the catalyst comprising the metallic compound supported on an inorganic compound carrier.
The method as disclosed in Japanese Patent Laid-Open No. 9-87215 (1997) uses an expensive imide catalyst and therefore is not satisfactory in cost. The method as disclosed in WO9940055 involves the step of preparing the solid catalyst and therefore is not efficient.